How might the egg shell be helpful to a developing chicken?

Answer 1

Humans and other animals have used eggs as a food source for many centuries. Today, we associate the hen’s egg so much with its role as food that it is easy to overlook the fundamental biological role of the egg.The hen’s egg as an incubatorNature’s role for the egg of the laying hen is as an incubation chamber for the developing chicken. For an egg to develop into a chicken, it needs to have been fertilised by a rooster (also called a cockerel).Once the fertilised egg is laid, it must be kept warm. This may be done naturally by the hen sitting on the egg, or artificially by placing the egg into an incubator.The egg contains all the nutrients that the developing chick needs during the three-week incubation period and also for the first couple of days after hatch. Water vapour and the gases oxygen and carbon dioxide are able to move across the egg shell through small openings called pores.The developing chick starts off as a single fertilised cell on the surface of the yolk and progressively grows, using up the yolk, some of the albumen and some calcium from the inside of the egg shell. In the final stages of development, the chick takes up the last bits of yolk into its own digestive system.Figure 1. Cross section of an egg as incubatorThe hen’s egg as a table eggEggs that are produced commercially for the purposes of eating have not been fertilised by a rooster. Therefore, they cannot develop into chickens.The production of the bird egg consists of a series of steps that occur as the egg enters and passes along the hen’s reproductive tract (oviduct). The yolk of the egg enters the top of the oviduct and passes into the infundibulum where it spends about 15 minutes. A membrane is added around the yolk and, if the hen has been inseminated, fertilisation occurs in this section of the oviduct. The yolk then spends about three hours in the magnum where the egg white is formed and then one hour in the isthmus where the shell membrane is laid down. The main part of the egg shell is formed in the tubular shell gland and the shell gland pouch and this takes about 20 hours. The egg shell is sometimes referred to as a bio-ceramic because it is made up of calcium carbonate with an organic matrix running through it.

Answer 2

The shell is pourous, allows heating and cooling easier. The shell protects the developing chick.